Abstract

We demonstrate aqueous refractive index sensing with 15–30 μm diameter silicon nitride microdisk resonators to detect small concentrations of Li salt. A dimpled-tapered fiber is used to couple 780 nm visible light to the microdisks, in order to perform spectroscopy on their optical resonances. The dimpled fiber probe allows testing of multiple devices on a chip in a single experiment. This sensing system is versatile and easy to use, while remaining competitive with other refractometric sensors. For example, from a 20 μm diameter device we measure a sensitivity of 230 ± 20 nm/refractive index units (RIU) with a loaded quality factor of 1.5 × 104, and a limit of detection down to (1.3 ± 0.1) × 10−6 RIU.

The authors thank J. M. Gibbs-Davis for helpful discussions and supplying LiCl, and A. Darlington for help preparing the solutions. We thank A. J. R. MacDonald and B. D. Hauer for mentoring B.C.L. under the support of WISEST. This work was supported by the University of Alberta, Faculty of Science, NSERC Canada, Alberta Innovates Technology Futures, and the Canada Foundation for Innovation.